Bomac 1B38 S-band pre-TR Cell, frequency range 2.7 to 2.91GHz. This measures 81x38mm by 42mm deep. The window is 48x22mm, and it weighs approx 400g.

The 1B38 was developed in late 1943 and has a 1MW capability. It is filled with a mixture of argon and water vapour at approx 1cm Hg. It was typically used in tandem with a 1B27.